The present invention concerns the field of drip irrigation and more particularly a method for simultaneously manufacturing at least two conduits and an intermediate product allowing such conduits to be obtained.
There is known from U.S. Pat. No. 5,106,021, a drip irrigation conduit made from an elongated sheet of plastic material folded over lengthwise. The two plies are joined by their edges to form two longitudinal lips, which extend adjacent to the tube from which they are formed. When the tube is connected to a pressurised water source, it swells up and then has a cylindrical shape of circular section for example, from which the two lateral lips project.
One or both of the two lips of this conduit are provided with impressions, which form water flow cavities. These cavities have the shape of labyrinths, which, via water feed and discharge chambers, respectively communicate with the inside of the conduit and the exterior. These impressions are typically obtained by embossing or directly printing the plastic material using, for example, a roller including raised shapes on its periphery.
Such a conduit has acceptable flow qualities if the water with which it is fed is of irreproachable purity, for example if it is subjected to careful filtering, which is rarely the case of water used for irrigation. The shape of the labyrinths, whose outlines can only be defined approximately because of the very method via which they are made, does not allow a sufficiently turbulent flow of water, which leads to the labyrinths becoming quickly dirty and sooner or later blocked up.
Another drawback of this type of conduit lies in the fact that, making the labyrinths by embossing or printing does not enable a precise and regular shape to be obtained over the entire length of the labyrinths and their feed and discharge chambers, which is detrimental to the uniformity of the irrigation.
There is also known from U.S. Pat. No. 4,430,020, an irrigation conduit provided with two lips superposed on each other between which a resilient strip is inserted, connected in a watertight manner to said lips. Flow cavities each including a feed chamber in communication with the inside of the conduit and a discharge chamber in communication with the exterior are arranged at intervals in the strip. This document does not, however, describe how to manufacture such an irrigation conduit continuously, or how to manufacture at least two irrigation conduits simultaneously.
There is also known from Patent No. EP 0 642 915, a method for simultaneously manufacturing at least two Irrigation conduits. According to this Patent, two conduits are formed side by side and connected to each other by a junction section including, according to a first embodiment (shown in FIG. 5), a plurality of pre-formed members in the form of a strip fixed inside the junction section at intervals along the longitudinal axis of the conduits. Each pre-formed member includes a pair of flow-reducing cavities, located respectively on either side of the longitudinal axis of the pre-formed member. Each cavity includes a feed chamber and a discharge chamber between which there extends a labyrinth-shaped channel, the discharge chambers of each cavity of a pair communicating with each other. The junction section of the conduits is then slit along the longitudinal axis of the pre-formed members to form two irrigation conduits each including a plurality of flow cavities.
According to the embodiment in question, the cavities are made in the strip by embossing the material of strip to form a impression of determined shape, the impression including in all cases a bottom formed by a portion of the strip. This technique for shaping the cavities does not guarantee satisfactory integrity of the geometry of the cavities and leads to the drawbacks already mentioned with reference to U.S. Pat. No. 5,106,021. The method disclosed in Patent No. EP 0 642 915 does not satisfactorily answer the expectations and requirements of users.
The main object of the invention is to overcome the drawbacks of the prior art by providing a simultaneous manufacturing method for at least two irrigation conduits which can easily-be implemented and which ensures economical and continuous manufacture of irrigation conduits able, in particular, to be used with imperfectly filtered water without any risk of clogging.
The invention therefore concerns a method for simultaneously manufacturing at least two irrigation conduits including the steps consisting in:
a) continuously producing at least a strip made of plastic material,
b) cutting out by stamping, in said strip through flow cavities, substantially on either side of a longitudinal plane of symmetry of the strip each flow cavity including at a first end a feed chamber intended to open out into one of said conduits and at another end a discharge chamber intended to open out on the exterior of said one conduit the stamping step being also provided so that the discharge chambers of the flow cavities extend substantially on either side of the plane of symmetry of the strip and the discharge chambers of the flow cavities located respectively on either side of the plane of symmetry do not communicate with each other,
c) continuously producing a tubular sleeve made of plastic material intended to form said conduits,
d) guiding said strip axially inside said sleeve during its production,
e) pinching said sleeve in at least a diametral zone to form an elongated two-part body exhibiting symmetry with respect to a longitudinal plane and including two juxtaposed conduits, joined by superposed bands integral with said sleeve, said trip being secured in an impervious manner between the bands,
f) bonding said strip to said bands, and
g) slitting said two-part body longitudinally along said plane of symmetry.
This method leads to continuous manufacturing of conduits without requiring the use of discrete flow reducing member or dripper units well known in the prior art, such as those described in U.S. Pat. No. 5,163,622, such dripper units requiring manufacturing, handling, guiding, orientation and transport control until they are inside the conduit.
It will be noted especially, that, owing to the implementation of the stamping step, it is possible to obtain flow cavities or labyrinths having very precisely defined geometries, allowing, in particular, turbulence to be created in the water which passes through them causing a self cleaning of the cavities and a limitation of the flow rate. Further, it becomes convenient to give each cavity a significant length, which also contributes to improving the self cleaning properties. Finally, the shape of the cavities is perfectly reproducible so that regular irrigation is obtained over the entire length of the conduit.
Moreover, the fact that the discharge chamber of the cavities located substantially on either side of the plane of symmetry of the strip do not communicate with each other allows the flow channels to keep their geometrical integrity during the entire manufacturing process. Indeed, without this feature, the portion of strip arranged between the channels of each flow cavity would overhang and could move laterally inducing thereby variations in the dimensions and geometry of the channels of the labyrinth which would affect the flow rate and could possibly block the channels.
Other advantageous features of this method are defined in dependent claims 2 to 10.
The invention also concerns an intermediate product obtained according to the invention, said intermediate product being steps a) to f) of claim 1 characterised in that it includes an elongated two-part body exhibiting symmetry with respect to a longitudinal plane and including two juxtaposed conduits joined by superposed bands integral with said sleeve, and a strip fixed in an impervious manner between the bands, in that said strip is provided with through flow cavities, substantially on either side of said longitudinal plane of symmetry of the strip, each flow cavity including at a first end a feed chamber opening out into one of said conduits and at another end a discharge chamber intended to open out to the exterior of said one conduit and in that the discharge chambers of the flow cavities extend substantially on either side of the plane of symmetry of the strip and in that the discharge chambers of the flow cavities located respectively on either side of the plane of symmetry do not communicate with each other.
This intermediate product has the advantage of considerably facilitating the manufacture of irrigation conduits and reducing the cost thereof because of the possibility of manufacturing two conduits simultaneously.